As is known in the art, one common approach to electronically control the valve actuation of an internal combustion engine is to have two electromagnets toggle an armature connected to the valve between an open position and a closed position. More particularly, referring to FIG. 1, when a first, here upper, one of the electromagnets is activated, the armature is attracted to the activated electromagnet thereby driving the valve to move to its closed position. Also, as the armature is attracted to the activated electromagnet, a first spring, in contact with the upper end of the armature is compressed. When the first electromagnet is deactivated, the first compressed, spring releases its stored energy and drives the armature downward thereby driving the valve towards it open position. As the armature approaches the second, lower, electromagnet, the second electromagnet is activated driving the valve to its full open position. It is noted that a second, lower spring becomes compressed during the process. After becoming fully open, the second electromagnet is deactivated, and the lower spring releases its stored energy to thereby drive the armature towards its upper position, the first electromagnet is activated and the process repeats. Thus, the two electromagnets toggle the armature connected to the valve between an open or closed position where it is held, while the pair of springs is used to force the valve to move (oscillate) to the other state (FIG. 1).
One problem with the approach described above is that, in the presence of high friction or gas force loads on the valve, the magnets must generate force over a significant fraction of the valve stroke. At points of travel where the gap (i.e., the “air gap”) between the activated magnet and the portion of the armature experiencing the magnetic force produced by the activated electromagnet (i.e., the attractive magnetic force) is large, high current is required to achieve the required attractive forces. This increases power consumption. The peak force that can be practically generated is reduced as the air gap increases thereby effectively reducing the authority to control the valve motion.
As noted from FIG. 1, with the exception of a small lash gap δ between the armature and valve stem at the closed position, there is a one-to-one relationship between the distance, Z, traveled by the armature and the distance traveled by the valve. Thus, from a neutral position Z=0 shown the middle portion of FIG. 1, to the fully closed position, shown in the left portion of FIG. 1, the armature moves a distance, Z=−L/2. Likewise, from the neutral position shown the middle portion of FIG. 1, to the fully closed position, shown in the right portion of FIG. 1, the armature moves a distance, Z=+L/2. Thus, the armature moves a distance of L and the valve moves a distance L-δ during each open-close cycle.
An alternative to this direct acting linear (i.e., one-to-one) oscillator, is shown in FIG. 2. Here, the actuator uses a mechanical lever to amplify the travel distance of the armature and thereby reduce the effective air gap. For example, with the magnets disposed about half way along the lever arm, such portion of the lever arm need only be displaced a distance L/2 in order to achieve a valve displacement of L-δ during an open-closed valve cycle. As a result of the reduced gap, the lever system does improve the control authority through the stroke and improves the power consumption relative to conventional linear oscillators.
However, as is also known in the art, existing designs have limited peak engine operating speed due to limited valve transition times (i.e., time from fully open to fully closed or vice-versa). For good durability and low noise, existing designs require complex feedback control algorithms to achieve low impact velocities during valve seating, armature seating, and lash take-up. Control schemes to date use high-speed (approximately 10-50 kHz control loop frequencies) computing power, and high-resolution position and current sensors for each valve. The algorithms are highly complex, and will likely require adaptive or iterative learning control schemes to both reduce calibration effort and to compensate for changes in actuator and valve characteristics over the life of the engine. To date, the poor robustness and high cost of such schemes make implementation impractical. The systems shown in FIG. 1 and FIG. 2 do not address issues of passive lash management or passive damping and have limited packaging flexibility and ability to optimize the design.